1. Field of the Invention
The present invention relates to apparatus and a method for increasing the utility of a cellular radio communication system. More particularly, this invention pertains to a microprocessor controlled interface that renders numerous useful devices compatible with existing cellular systems.
2. Description of the Prior Art
Mobile telephone communication technology has grown from one way radio transmission, much like that of the Citizens Band (C.B.), to fully-duplexed audio, both voice and data. In large measure, the progress of this technology has followed from the development of low power transmissions that have increased the number of user (and useable) frequencies.
A further development in the area of mobile telephone communication has been that of the cell theory of radio transmission. Cellular systems currently utilize 666 channels assigned by the FCC in an 850 MHz frequency band. Half of such channels are reserved for wire line carriers (local operating companies).
In a cellular system, the service area is divided into a plurality of cells of 8 to 12 miles in radius. The cells may be further subdivided in accordance with the projected amount of system traffic. As the available frequencies are apportioned among an increased number of cells, the required operating power decreases.
Communication by means of a cellular system requires, inter alia radio contact between the mobile vehicular equipment and cell site transmission and receiving equipment. Land line facilities are utilized to tie the vehicular-cell site link into a conventional central switching office whereby the mobile unit is patched into either a non-mobile, "conventional" telephone (or modem) or another mobile telephone so that a full-duplex communication link is established.
The vehicle mounted apparatus of the mobile cellular system commonly comprises a mobile transceiver and a handset. The handset and the transceiver communicate through a logic bus whereby the transceiver is activated to transmit audio entered, as either voice or data, into the handset and to transfer audio and signalling received from the cell site transmission and receiving equipment. In existing mobile systems, the user must become familiar with the particular operational characteristics and requirements of the handset which are differ from that of the standard dial or touch telephone. For example, one must become familiar with a telephone receiver (the handset) that has a peculiar audio "call in" signal that is quite different from the sound of the electromechanical telephone ringer. One must also adjust to a receiver that is totally mute prior to completion of a connection, sounding as if it were a dead line and providing no indication prior to the completion of dialing that the vehicle has entered a "no service" area. The user must become fully conversant with the handset keypad functions, assiduously entering a manual "send" command when initiating a communication. Of further concern, the handset and the transceiver must be "matched" in accordance with the applicable protocol of the manufacturer, further limiting the options of the user.